diff --git a/Modules/_dbmmodule.c b/Modules/_dbmmodule.c
index 57755111a6a..80c73bf0da2 100644
--- a/Modules/_dbmmodule.c
+++ b/Modules/_dbmmodule.c
@@ -2,6 +2,7 @@
 /* DBM module using dictionary interface */
 
 
+#define PY_SSIZE_T_CLEAN
 #include "Python.h"
 
 #include <sys/types.h>